Meanwhile, boil potatoes in water 15 minutes or until fork-tender. Drain and mash potatoes. In large bowl, mix mashed potatoes, flour, 1 tablespoon sugar, and 3/4 teaspoon salt to make a soft dough. On lightly floured surface, knead dough until smooth and slightly sticky. Cut dough into 12 pieces. Roll each piece into a 1/2-inch-diameter log. With floured fork, make indentations all the way down each log. Cut logs into 1 1/4-inch pieces (gnocchi).

In 5-quart saucepot over high heat, heat 4 quarts water to boiling. Add gnocchi. With slotted spoon, carefully remove gnocchi to platter as soon as they start to float. Spoon marinara sauce over gnocchi. If you like, sprinkle with Parmesan cheese.